COORDINATES & PROJECTIONS

G001

Sphericalcoordinates☼Angles☼ Latitude☼ Longitude

G103

Ellipsoids

☼Major axis☼Minor axis☼ Flattening ratio

G001

Geoids

☼Uneven surface

☼Bumps & dimples

G106

Geoidal height G060

Earth surfacesG058

Datums

☼Starting point for measuring Earth’s size☼Basis for grid systems☼Based on different ellipsoids☼NAD27☼NAD83 ( GRS80)☼WGS84

Comparing datumsG061

Geographicgrid☼ Latitude☼ Longitude☼Poles☼Meridians☼Parallels

G108

Units aredegrees☼N, +☼S, –☼ E, +☼W, –☼dd°mm' ss"☼dd.dddd°

G104

Making Earth flat

☼3 dimensions☼2 dimensions☼Projections

G057

Coordinate systems

☼Geographic: longitude, latitude

☼Cartesian (planar): x, y

☼ “read right up”

G102

Projection☼3D 2D☼ Ideals

Angles(shapes)

Distances

Directions

Areal sizes

☼Compromise: “best” depends on use☼http://www.radicalcartography.net/index.html?

projectionref

G401

Variables in projections

☼Class (cylindrical, conical or azimuthal)

☼Point of secancy (tangent or secant),

☼Aspect (normal, transverse or oblique)

☼Distortion property (equivalent, equidistant or conformal)

Classes of projectionsG053

Secancy of projectionsG054

Aspects of projections

G055

(Non-) distortion properties of projections

☼Conformal: angles, small areas

☼ Equivalent: area (but not shape)

☼ Equidistant:

Conformal projections (e.g. Mercator)☼N/S - E/W lines

always perpendicular

☼Areas distorted☼Distortion

increases with larger areas

☼Good for tracking motion or change in location

G051

Equal area ("equivalent") projections

☼Areas(length × width) accurate

☼Angles (shape) not accurate

G052

Equidistant projections

☼Constant scale

☼Uses “standard” parallels or points

☼Distances accurate (sometimes)

G056

Comparing projections G110

Suggested projections for given tasks/areas☼ Whole Earth: Robinson (pseudocylindrical) or Miller Cylindrical

☼ Hemispheres: Orthographic (azimuthal), Lambert Azimuthal Equal Area

☼ Continents: Lambert Conformal Conic (North America, Eurasia); Lambert Azimuthal Equal Area or Orthographic (South America, Africa); Orthographic (Australia, Antarctica)

☼ E-W Countries, Regions: Lambert Conformal Conic (US, Canada, Russia, China); Lambert Conformal Conic or Orthographic (Europe); Orthographic, Lambert Azimuthal Equal Area

☼ Polar Regions: Orthographic, Lambert Azimuthal Equal Area

☼ Oceans: Orthographic, Lambert Azimuthal Equal Area

☼ Smaller Countries or Regions: Orthographic

☼ N-S Countries, Oblique Regions: Transverse Mercator (long, thin countries aligned North-South such as Chile); Oblique Mercator (oblique regions like the Alaska panhandle)